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<title>Issue 4099: The simple case of views::as_rvalue and views::common are not strictly correct</title>
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<p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#New">New</a> status.</em></p>
<h3 id="4099"><a href="lwg-active.html#4099">4099</a>. The simple case of <code>views::as_rvalue</code> and <code>views::common</code> are not strictly correct</h3>
<p><b>Section:</b> 25.7.7.1 <a href="https://wg21.link/range.as.rvalue.overview">[range.as.rvalue.overview]</a>, 25.7.20.1 <a href="https://wg21.link/range.common.overview">[range.common.overview]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a>
 <b>Submitter:</b> Hewill Kang <b>Opened:</b> 2024-05-10 <b>Last modified:</b> 2024-06-24</p>
<p><b>Priority: </b>4
</p>
<p><b>View all other</b> <a href="lwg-index.html#range.as.rvalue.overview">issues</a> in [range.as.rvalue.overview].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p>
<p><b>Discussion:</b></p>
<p>
Currently, these two adaptors return <code>views::all(E)</code> when the type of subexpression <code>E</code> 
models <code>common_range</code> or its reference is the same as the rvalue reference.
<p/>
However, the current wording does not require that a <code>const</code>-qualified object of a <code>range</code> 
type must have the same non-commonality or value category of the reference as the non-<code>const</code> one,
this makes it theoretically possible for these two to still return non-common ranges or ranges whose reference 
are lvalue when acting on a <code>const</code>-qualified lvalue <code>view</code> object, because 
<code>views::all(E)</code> will remove the <code>const</code>-qualifier.
<p/>
The proposed wording pedantically checks <code>views::all_t&lt;decltype((E))&gt;</code> instead of <code>decltype((E))</code>.
</p>

<p><i>[2024-06-24; Reflector poll]</i></p>

<p>
Set priority to 4 after reflector poll.
"Not aware of any use case for making <code class='backtick'>const</code> affect those properties".
</p>



<p id="res-4099"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N4981" title=" Working Draft, Programming Languages — C++">N4981</a>.
</p>

<ol>

<li><p>Modify 25.7.7.1 <a href="https://wg21.link/range.as.rvalue.overview">[range.as.rvalue.overview]</a> as indicated:</p>

<blockquote>
<p>
-2- The name <code>views::as_rvalue</code> denotes a range adaptor object (25.7.2 <a href="https://wg21.link/range.adaptor.object">[range.adaptor.object]</a>).
Let <code>E</code> be an expression and let <code>T</code> be <code>decltype((E))</code>. The expression
<code>views::as_rvalue(E)</code> is expression-equivalent to:
</p>
<ol style="list-style-type: none">
<li><p>
(2.1) &mdash; <code>views::all(E)</code> if <code>same_as&lt;range_rvalue_reference_t&lt;<ins>views::all_t&lt;</ins>T<ins>&gt;</ins>&gt;,
range_reference_t&lt;<ins>views::all_t&lt;</ins>T<ins>&gt;</ins>&gt;&gt;</code> is <code>true</code>.
</p></li>
<li><p>
(2.2) &mdash; Otherwise, <code>as_rvalue_view(E)</code>.
</p></li>
</ol>
</blockquote>

</li>

<li><p>Modify 25.7.20.1 <a href="https://wg21.link/range.common.overview">[range.common.overview]</a> as indicated:</p>

<blockquote>
<p>
-3- The name <code>views::common</code> denotes a range adaptor object (25.7.2 <a href="https://wg21.link/range.adaptor.object">[range.adaptor.object]</a>).
Given a subexpression <code>E</code>, the expression
<code>views::common(E)</code> is expression-equivalent to:
</p>
<ol style="list-style-type: none">
<li><p>
(3.1) &mdash; <code>views::all(E)</code>, if <del><code>decltype((E))</code></del><ins><code>views::all_t&lt;T&gt;</code></ins> 
models <code>common_range</code> <del>and <code>views::all(E)</code> is a well-formed expression</del>.
</p></li>
<li><p>
(3.2) &mdash; Otherwise, <code>common_view{E}</code>.
</p></li>
</ol>
</blockquote>

</li>
</ol>






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